1. Field of the Invention
This invention relates to a light-emitting display device for displaying a numeral or character in seven segments or in a dot matrix structure using light emitting elements such as LEDs, which is used for displaying an amount of money in a vending machine. More specifically, this invention relates to a light emitting display device having a simple structure which includes a lead frame or resin circuit board and a reflecting case and is difficult to produce diffraction of light due to peeling of the coating of the display surface of the reflecting case or light leakage from its rear face. Further, this invention relates to a light emitting display device whose vertical direction can be easily known when it is attached to a circuit board, thereby facilitating its mounting, and can prevent leak of light from between display devices arranged in plurality.
2. Description of the Related Art
A conventional light-emitting display device having a seven-segment structure has structured as shown in FIG. 7. In this structure, a light conducting portion constituting seven segments is formed in a reflecting case. For each segment, a light-emitting element (hereinafter referred to as xe2x80x9cLEDxe2x80x9d) not shown is die-bonded or wire-bonded onto a lead frame or resin circuit board. The light conducting portion is filled with light-permeable resin 4. The LED has an anode and cathode and hence must have two lead wires for each segment. In this case, the one lead wire for the anode or cathode may be common to the respective segments. Therefore, 8-10 lead wires (inclusive of that for a decimal point) are formed to exhibit a numeral of one digit. Namely, a plurality of lead wires 1 are provided along two long sides in a longitudinal direction (both sides in a display direction) or both upper and lower sides.
In order that the light emitted from the LED illuminates more brightly over the entire segment, the interior of the light conducting portion must be colored in whitish light-reflective color. Therefore, the reflecting case is generally made of whitish resin. Further, where the display surface is not a dark color such as black, the display color of each segment is difficult to recognize. For this reason, the surface of the reflecting case, as the case may be, the side thereof also is coated in the dark color such as black. The black coating is generally made in such a manner of drying black ink printed by screen printing.
As described above, in the light emitting display device for a numeral, its reflecting case is made of a whitish mold and the display surface is coated with a dark color such as black. However, the coating strength in the coating on the resin surface is not constant owing to the dirt of the surface state or reduction in flatness such as a projection due to a molding die. Therefore, the friction for the surface during transfer or contact therewith by handling during mounting is likely to produce scratching. Such a scratch leads to peeling of the black coating, exposes the underlying whitish resin and greatly deteriorates the appearance of the display surface.
Further, where the display is made on the arrangement of a number of units, not only the display surface but also the side surface is preferably coated with black because white on the side surface is difficult to see. However, the coating of the side surface causes the front and side surface rectangular prism to be coated by screen printing. In this case, the coating must be done for each surface. This greatly increases the number of man-hours of coating and the production cost. In addition, the problem of coating peeling still remains. Further, on the side of the bottom surface of the reflecting case, the case portion of the outer periphery and bottom surface to which a lead frame or resin circuit board portion is attached have different heights so that the entire bottom surface is not flat but complicatedly rugged. Therefore, it is very difficult to coat the bottom surface. The light which leaks toward the bottom via filled resin repeats random reflection between the whitish case of the bottom and the whitish lead frame plated with silver or resin circuit board having a metallic pattern so that light leakage occurs outside of another segment or the reflecting case. This is likely to produce erroneous exhibition. Where the reflecting case is formed of whitish resin, revived resin cannot be used since it cannot give white with high reflection coefficient. Namely, resources cannot be efficiently used.
Further, the light emitting display device for displaying numerals has the same appearance even when it is turned upside down where it has no decimal point. However, the lead connection is not necessarily symmetrical. Therefore, with its direction known correctly, the device must be mounted. In this case, since the appearance is entirely symmetrical, it is very difficult to know its direction.
In the light emitting display device such as a numeral display, a few of device units are arranged side by side to exhibit many digits. In this case, the device units must be arranged with no gap. However, for permission of the clearance during the process for manufacturing the device, and during its mounting, the gap of at least 0.1 mm or more must be given between the device units. Therefore, the gap between the adjacent device units cannot be removed completely. Meanwhile, in the light emitting display device with a reflecting case inclusive of its bottom coated with resin, the light emitted from the LED leaks to the bottom side of the reflecting case via the resin and the leaked light further leaks from the gap between the light-emitting display device units so that erroneous recognition of apparently exhibiting xe2x80x9c1xe2x80x9d between numerals occurs.
Further, in this kind of light emitting display device, its surface exclusive of e.g. segments of a numeral is colored in black to provide the good appearance. However, the light conducting portion in the vicinity of the LEDs is preferably colored in white to prevent absorption of light, thereby improving the display luminance. For this reason, the reflecting case is generally formed of whitish plastic and the surface of the display screen and its side surface as necessary are coated with black. On the other hand, where this light emitting display device is transferred, several tens of device units housed in a tube (stick) of plastic are transferred. In this case, at the time of taking in and out or where there is an internal clearance, the display screens of the device units are rubbed in the tube during the transfer. As a result, the coating may be peeled so that the display quality will be deteriorated.
This invention has been accomplished in order to solve the problem described above. An object of this invention is to provide a light-emitting display device which can reduce light leakage by coloring the reflecting case inclusive of the bottom in a light-absorbable color, thereby preventing erroneous exhibition.
Another object of this invention is to provide a light-emitting display device having a structure in which white is not exposed even when slight scratch is produced on the display surface so that the display surface is not spotted.
Still another object of this invention is to provide a light emitting display device having a structure in which revived resin can be used for the reflecting case.
Further, this invention has been accomplished in order to solve the above problem. An object of this invention is to provide a light emitting device whose vertical direction can be easily known.
Still yet another object of this invention is to provide a light emitting display device in which erroneous recognition of exhibition due to the leakage of light from gaps between a number of device units does not occur.
Still further object of this invention is to provide a light emitting display device in which the coating on the display screen owing to rubbing is not peeled and the display quality is not deteriorated.
Further yet another object of this invention is to provide a light emitting display device in which a plurality of the same device unit constituting a single display device such as a numeral display device can be mounted on a circuit board in a state where they have been previously arranged as necessary device units.
The light emitting display device comprises: a plurality of light-emitting elements for lighting parts of a display image, respectively; a plurality of leads to the one ends of which the light emitting elements are die-bonded or wire-bonded, respectively; a reflecting case which has light conducting areas corresponding to the parts of the display image and covers areas to be bonded; and light permeable resin filled in the reflecting case so that the light conducting portions of the reflecting case encircle the corresponding light emitting elements and the one ends of the plurality of leads are fixed. In the light-emitting display device, the reflecting case is made of resin, and the inner walls of the light conducting portions are colored in a light-reflective color whereas the remaining outer surface of the reflecting case inclusive of the bottom is colored in light-absorptive color.
Now, the display image means an image which can change the display state of a numeral, character, etc. A part of the display image means one segment in the case where e.g. a numeral is exhibited using seven segments. The light reflective color means a whitish light-reflective and blight color such as white and light gray. The light absorptive cooler means a blackish, difficult to reflect, dark color such as black and navy blue.
In accordance with this invention, the reflecting case inclusive of its bottom is colored in the light absorptive color. For this reason, even when light emitted from the LED leaks via the light-permeable resin toward the bottom of the reflecting case and reflects from the lead frame inserted on the bottom side, it is absorbed on the bottom side. Therefore, random reflection of the light is not repeated therebetween. As a result, the light does not leak into an adjacent segment or the outside of the reflecting case.
In another embodiment of the light-emitting display device according to this invention, it is not required in the above configuration that the entire surface inclusive of the bottom other than the light conducting portions is colored in the light-absorptive color as long as the reflecting case is made of resin with the light-reflective color and at least the surface thereof on the side of a display surface is impregnated with dyes with a light absorptive color. In this configuration, even if the display surface is scratched and rubbed by a transfer case, the light absorptive color on the display surface does not disappear so that the whitish color is not exposed nor spotted. Specifically, since the resin is impregnated (dyed) with the light absorptive dyes to its interior, the dyes soak to a certain depth from the surface. Therefore, even if the flaw due to scratching is created on the display surface, the whitish color does not appear. Incidentally, the word xe2x80x9cimpregnationxe2x80x9d means that the dyes soak to the depth of 10 xcexcm or more from the surface of the resin to dye the resin.
In still another embodiment, the reflecting case may be made of resin with a light-absorptive color, and the inner walls of the light conducting portions may be processed in a light-reflective color. For this reason, revived resin can be used. The entire surface inclusive of the bottom other than the light conducting portions can also be colored in the light-absorptive color. Further, the diffraction of light can be prevented at the bottom. Moreover, since the reflecting case is made of the same dark color material to its interior, even if there is a deep flaw, the display surface is colored in the same color but not spotted. Additionally, the inner walls of the light-conducting portions can be colored in the light reflective color by spraying of whitish paint, non-electronic plating of e.g. Ag or impregnation of white dyes, etc.
The invention in which the surface of the resin with the light reflective color is colored in the light absorptive color by impregnation or the interiors of the light conducting portions in the resin with the light absorptive color is colored in the absorptive color can be employed.
The structure proposed according to this invention permits a person to know the direction of the light emitting display device from the outer shape of the reflecting case. The correct direction of the light emitting display device can be easily known through automatic recognition by a camera and the sense of touch by a man""s hand. Therefore, the light emitting display device can be very easily mounted on a circuit board. Further, the uneven portions can be formed so that they have opposite steps on the upper and lower surfaces of the reflecting case or the left and right surfaces thereof. In this configuration, where the light emitting display devices are arranged vertically and/or horizontally, these steps are caused to overlap so that erroneous recognition of a exhibited numeral, which is attributed to leakage of light from the gap between adjacent light emitting display devices when light leaks to the rear surface of the reflecting case, does not occur. Further, uneven portions can be formed, for example, on the upper and lower surfaces thereof or the left and right surface thereof so that they are engaged with one or more linear projections formed on inner side walls of a tube which is used to transfer the light emitting display device. In this configuration, since the display screen of the light emitting display device is not rubbed within the tube, and leads are not housed within the tube so that the coating on the display screen will not be peeled.
For example, the reflecting case is substantially square in shape of the display screen of the display image, and the uneven portions are formed in such a manner that steps are formed at least left and right side walls thereof in a longitudinal direction of the display image so that the reflecting case can partially overlap an adjacent reflecting case between light emitting display devices arranged horizontally, or otherwise projections are formed at least on the upper and lower surfaces thereof or the left and right surface thereof in a longitudinal direction of the display image so that they are engaged with one or more linear projections formed on inner side walls of a tube which is used to transfer the light emitting display device. Incidentally, the left/right or upper/lower in a longitudinal direction of the display image means those in a state generally viewed when a numeral or character is displayed.
Preferably, the reflecting case is substantially square in shape of the display screen of the display image, and has uneven portions formed at least left and right side walls thereof in a longitudinal direction of the display image so that they can be fit into/over those of an adjacent reflecting case between light emitting display devices arranged horizontally. In this configuration, for example, where display device units are arranged to a single light emitting display device, the device units integrated by fitting between the uneven portions can be collectively mounted on the circuit board. This simplifies the mounting and interrupts light leakage from the boundary between adjacent light emitting display device units, thus improving the display quality.
Preferably, the plurality of leads are extended out from the upper surface and lower surface of the reflecting case in a longitudinal direction of the display image and bent at an approximately right angle to the surfaces of the leads to be bonded at their one ends and further bent so as to be substantially parallel to the surfaces at their other ends. In this configuration, the light emitting display device units which are arranged generally horizontally can be intimately arranged horizontally and the problem of contact between the leads does not entirely occur. For this reason, the light emitting display device can manufactured using a lead frame. In addition, where the tips (other ends) of the leads are bent for surface-mounting, the device can be formed into the surface-mounting type having a gull-wing shape in which the leads are bent outwardly but not inwardly (beneath of the resin). The leads can be also formed into a structure from which the state of soldering can be easily recognized. Incidentally, bending the leads at a substantially right angle to the surfaces of leads to be bonded does not mean to bend them at an accurate right angle, but the greater part of the leads in a bending direction is in the direction of the right angle.